1. Field of the Invention
This invention relates generally to a control system for estimating the tongue length of a trailer being towed by a vehicle and, more particularly, to a control system for estimating the tongue length of a trailer being towed by a vehicle where the trailer includes a yaw rate sensor, and where the vehicle includes driver operated front-wheel steering with or without computer controlled rear-wheel steering.
2. Discussion of the Related Art
Automotive vehicles that employ coordinated front-wheel steering and rear-wheel steering systems are known in the art. Typically in such coordinated vehicle wheel steering systems, the driver controls the steering of the vehicles front wheels and a computer-based on-board steering controller controls the steering of the vehicles rear wheels in response thereto. In one example, the computer controlled rear-wheel steering system employs an electric motor-driven rack and pinion rear-wheel steering actuator.
Backing up a vehicle-trailer is typically a complex task, and requires a significant level of skill. It is heretofore been known in the art to employ a coordinated front and rear-wheel steering system to assist a driver operating a vehicle pulling a trailer. Particularly, U.S. Pat. No. 6,292,094, issued Sep. 18, 2001 to Deng et al., assigned to the assignee of this application and herein incorporated by reference, discloses a vehicle/trailer backing up control system in connection with a computer controlled rear-wheel steering system. The '094 patent employs an algorithm that uses front-wheel angle, vehicle speed, vehicle yaw rate and hitch angle to control the rear-wheel steering angle to assist the operator in backing up the vehicle-trailer.
The vehicle-trailer back-up control system disclosed in the '094 patent has been shown to be effective in assisting the vehicle operator when backing up a trailer. However, because trailers come in a variety of different lengths, the performance of the back-up control system can be improved by providing an input to the system that gives an estimation of the tongue length of the trailer. The algorithm in the '094 patent uses the same average tongue length for trailers of all lengths.
U.S. patent application Ser. No. 10/336,120, filed Jan. 3, 2003, titled “Trailer Tongue Length Estimation Using a Hitch Angle Sensor,” assigned to the assignee of this application, and herein incorporated by reference, discloses a system that estimates the tongue length of a trailer being towed by using a hitch angle sensor that provides a measurement of the hitch angle between the vehicle and the trailer to determine the tongue length. That system has also been shown to be effective in estimating the tongue length of the trailer to improve the ability of the control system to assist the driver in backing-up the trailer. However, further improvements can be made to make the system more practical and more cost effective. For example, because trailer hitches come in a variety of styles, sizes, etc., providing a hitch angle sensor that accurately measures the hitch angle for all of the various types of hitches may be impractical and costly.